The momentum of the body is 12 m/s.
Momentum is the product of the mass of a body and velocity. According to Newton's second law, the rate of change of momentum is equal to the impressed force.
The details required to answer the first two questions are missing hence we can't answer those questions. For the last question;
p = mv
m = mass
v = velocity
p = momentum
v = p/m
v = 72,000 kgm/s/6,000 kg
v = 12 m/s
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